1. Field
The present application relates to electronic systems, and more particularly to X-ray detection arrays.
2. Description of the Related Technology
In X-ray crystallography and other natural and material sciences, an ongoing goal is the development of a high-dynamic-range, high-resolution, high-bandwidth imaging system. Currently, detector arrays are typically composed of either analog pixels, digital pixels, or mixed-mode pixels. Analog pixels, or photon integrating pixels, typically digitize charge accumulated on a capacitor caused by incident photons over an exposure period. Digital pixels count individual photons incident on the pixel during the exposure period. Because each photon is counted by discrimination logic, digital pixels tend to have lower noise for weak exposures. Furthermore, their design allows for room temperature operation. In contrast, analog pixels tend to have higher noise rates for weak exposures. On the other hand, digital pixels can only count as fast as their reset time, which is typically on the order of 100 ns. Thus, when two photons arrive within a short period of time, only one will be counted. This fundamental flux limitation can cause inaccuracies in strong exposures. Furthermore, digital pixels tend to have systematic errors when photons strike the corners of pixels because the charge split between pixels may not reach the detection threshold. Digital pixels also require recalibration when changing the energy of the photons.
Mixed-mode pixels combine some advantages of both the analog and digital pixels. Mixed-mode pixels allow charge to accumulate on a capacitor until it reaches a threshold, and then remove that charge. The number of times the charge reaches the threshold during the exposure period is counted, and any remaining charge at the end of the exposure period is digitized. Because mixed-mode pixels count charge ramps, they do not exhibit the same flux limitations of digital pixels. Similarly, there are no systematic errors when photons strike pixel corners because the charge distributed between the pixels is all accounted for. However, mixed-mode pixels have greater cooling needs, and read noise is still greater than digital pixels.
There is a need for improved imaging systems with high-dynamic-range and high-resolution, and methods for configuring those systems.